Gastrotrichs (hairy-backs) are
small (less than 4 mm), dorsoventrally flattened, transparent worms. At the
anterior end they have sensory bristles, cilia, sensory pits, and some species
have eye spots. The body ends in a tail or fork. Over 400 species are known.

They inhabit interstitial spaces in sand and compacted surfaces, and move using epidermal cilia to glide along, or
loop in a leech-like fashion using adhesive tubes, see Chaetonotus sp. on the right and below which has two adhesive tubes.

Males tend to be rare and
poorly developed.The marine species tend to be less well known, but their food is the same as Chaetonotus sp. below.

On the left is Chaetonotus maximus, a freshwater gastrotrich, and below another in the same genus. Chaetonotus sp. feeds on detritus, bacteria, diatoms and protozoa.